Biomimetic KcsA channels with ultra-selective K+ transport for monovalent ion sieving

Crown ether-functionalized metal organic framework biomimetic nanochannels membrane for efficient Tl+ ion transport and Tl+/Li+ sieving

Fueled by the new energy revolution, the demand for lithium has soared beyond its supply, with lithium mining and smelting emerging as a crucial source. In this process, thallium-containing wastewater is produced, causing environmental pollution. In this work, inspired by the biological K+ ion channel, which preferentially transports Tl+ due to its similarity to K+, we constructed a conical single nanochannel (SCN) membrane modified with crown ether (4AB18C6) and MOF (UiO-66-(COOH)2) for Tl+ ultrafast transport, instead of Li+. The 4AB18C6/MOF-MCN exhibited the Tl+ permeation rate of 5.72 mmol m-2 h-1 at low concentrations, with a Tl+/Li+ selectivity of about 30 in the binary system. The shape and charge properties of the SCN itself, along with its specific binding with 4AB18C6/MOF for fast Tl+ transport. The competitive inhibition arising from the difference of Tl+ and Li+ dehydration in a binary system further enhances the Tl+ ion selectivity. This work provides an efficient approach to excellent Tl+ transport and sieving capabilities, potentially inspiring further research on Tl pollution and resource recycling in the lithium industry.

Potassium-Selective Covalent Organic Framework Membranes Enable Dynamic Monitoring of Microbial K+ Metabolism

Ultraselective and rapid transport of potassium ion (K+) is crucial for maintaining life activities such as osmotic pressure equilibrium, protein synthesis regulation, microbial growth, and communication. However, it is challenging to achieve high efficiency and precise K+ transport due to the existence of competitive cations with similar size and valence. Here, a biomimetic K+ nanochannel based on sulfonated covalent organic frameworks (COF) is reported with high K+ screening selectivity to achieve dynamic microbial K+ metabolism monitoring. Similar to the structure and function of biological KcsA channels, sulfonated COF feature ordered nanochannels and abundant surface charges, facilitating effective sieving of K+ and sodium ions (Na+) through size screening and electrostatic interactions, achieving a K+/Na+ selectivity ratio of 17.3. Molecular dynamic simulations indicate that the K+/Na+ selectivity of the COF nanochannels arises from the interaction of K+ with the sulfonate functional groups on the nanochannels, resulting in a decreased energy barrier for K+. Given the excellent K+ screening selectivity and efficiency, the designed COF nanochannels enable real-time monitoring of K+ in complex microbial systems and provide guidance for the synthesis of high value-added products. These findings suggest approaches for developing efficient and selective nanochannels for ion separation, nanofluidic, and complex microbial metabolism systems.

Concentration Energy Ion Channels with Molecular-Structure Dual Recognition for Sustainable Environmental Monitoring

Pesticides are vital for crop and seafood production but leave persistent residues that pose risks to ecosystems and human health through bioaccumulation. The detection of pesticide residues requires highly sensitive and selective technologies. Herein, a nanochannel sensor capable of dual recognition of ionic charge and molecular conformation based on molecular imprinting technology (MIT) is presented, offering a significant improvement in selectivity and sensitivity over traditional nanopore sensors. The MIT-based nanochannels with imprinting sites tailored to pesticide molecules go beyond recognizing the molecular size and surface functional groups, enabling the detection of molecular configurations. In this research, the approach enables the detection of 10 pesticide molecules with detection limits (LODs) ranging from 12.9 to 26.9 pM, achieving two orders of magnitude lower than fluorescence-based methods. Density functional theory (DFT) and molecular dynamics (MD) simulations revealed hydrogen bonding as the dominant interaction in the imprinting process. This versatile nanochannel construction method, proposed for the first time, provides dual recognition capabilities and is expected to advance nanochannel sensing while promoting sustainable environmental development.

Improving the ion sieving performance of MOF polycrystalline membranes based on interface modification

Metal-organic framework (MOF) membranes exhibit promising potential for high-precision molecule and ion sieving due to their uniform and tunable pore structures. Nevertheless, it remains a challenge to address interfacial compatibility to obtain a high-performance MOF membrane. This is because there is a weak interfacial interaction between the MOF and the substrate, which leads to non-selective areas. This work presents an interface-coating method to facilitate dense nucleation and rapid growth of MOF crystals on the substrate towards reinforcing interaction and eliminating defects. Polydopamine (PDA) and β-cyclodextrin (β-CD) were co-assembled on polyvinylidene fluoride (PVDF) substrates to modify the surface chemistry and enhance interfacial compatibility, thereby facilitating the dense growth of ZIF-8. The ZIF-8/PVDF membranes demonstrated an excellent K+ permeance of 0.33 mol m-2 h-1 and a K+/Mg2+ selectivity of 30.16. The simulation results indicate that the channel of Mg2+ through ZIF-8 must overcome a greater transport energy barrier than that of K+, resulting in a higher selectivity of K+/Mg2+.

Engineering Bipolar Covalent Organic Framework Membranes for Selective Acid Extraction

Nitric acid (HNO3) is a vital industrial chemical, and its recovery from complex waste streams is essential for sustainability and resource optimization. This study demonstrates the effectiveness of bipolar covalent organic framework (COF) membranes with tunable ionic site distributions as a solution for this challenge. The membranes are fabricated by layering anionic COF nanosheets on cationic COF layers, supported by a porous substrate. The resulting membranes exhibit significant rectifying behavior, driven by the asymmetric charge polarity and the intrinsic electric field, which enhances HNO3 transport. The transmembrane diffusion coefficient of 2.74 × 10-5 cm2 s-1 exceeds the self-diffusion rate of NO3 -, leading to increased HNO3 flux and selectivity compared to the individual anionic and cationic COF membranes. The optimized bipolar membrane configuration achieves remarkable separation factors, ranging from 22 to 242,000 for HNO₃, in comparison to other solutes such as HCl, H2SO4, H3PO4, and various metal salts in an eight-component mixed waste stream. This results in a substantial increase in HNO₃ purity, from 12.5% to 94.1% after a single membrane separation. With the broad range of COF materials and the versatility of the proposed membrane design, this work represents a significant advancement in chemical separation technologies.

Randomly oriented covalent organic framework membrane for selective Li+ sieving from other ions

Certain biological channels exhibit remarkable selectivity, effectively distinguishing between competing cations. If artificial membranes could achieve similar precision in differentiating competing ions from Li+, it could advance sustainable technologies in lithium extraction. In this study, we present a covalent organic framework (COF) membrane featuring a randomly oriented structure that enables selective separation of major competing ions from Li+. The random orientation results in narrow pores, which impart size-based selectivity among alkaline ions. Additionally, the COF incorporates sulfonic groups that preferentially bind to Na+ and K+, facilitating their transport while retaining Li+. These synergistic mechanisms endow the membrane with a selectivity beyond detection limit for K+ and Na+ over Li+. When driven by an electrical potential, the ion flux through the membrane is enhanced by over an order of magnitude. Notably, the membrane also permits the transport of Mg2+ and Ca2+ while still rejecting Li+, leveraging differences in their ion mobility. This work should advance the design and construction of biomimetic materials for the extraction of valuable species from seawater and other aqueous sources.

Selective acid recovery and metal separation from acid mine drainage using a highly stable vermiculite membrane

Selective ion separation from acid mine drainage (AMD) under extreme acidic conditions presents a critical environmental challenge. While membrane-based technologies show promise for advancing water treatment processes, implementation in AMD treatment requires membranes that combine exceptional acid stability with precise ion sieving capabilities. Inspired by the ion retention characteristics of natural clay minerals, we have developed cation-selective membranes using vermiculite nanosheets as building blocks. The vermiculite membranes (VM) featured high acid stability and well-ordered two-dimensional nanochannels (2 Å), achieving a high H+ permeation rate of 3.24 mol m-2 h-1. The VM demonstrated exceptional selectivity between monovalent and metals ions, with a H+/Fe3+ selectivity factor of 1284 in single-cation transport process. In complex multi-ion environments, the VM maintained stable separation performance, achieving a H+/Fe3+ selectivity of 1000 in mixed solutions containing H+, K+, Na+, Ca2+, Mg2+ and Fe3+. Additionally, VM effectively blocked other common AMD metals, including Cu2+, Co2+, Ni2+ and Mn2+, while maintaining stable separation performance even at extreme low pH values (pH = 1). Through integrated theoretical calculations and experiments, we revealed that the synergistic effects of ultra-confined nanochannels (4∼5 Å) and surface charge created enhanced energy barriers for trivalent ion transport, resulting in high ion selectivity. Beyond providing an effective solution for AMD remediation, this work establishes vermiculite-based membranes as promising candidates for ion separation applications.

Artificial Cation-Chloride Co-Transporters for Chloride-Facilitated Lithium/Magnesium Separation

Inspired by nature, many artificial ion sieving materials have been developed, shedding light on the next-generation ion, e.g., Li+, extraction applications. Artificial co-transporters remain difficult to construct since they have a much more complex ion-sieving property. For example, the cation-chloride co-transporters have both alkaline ion and chloride ion selectivity but no alkaline ion/chloride ion selectivity. We here demonstrate a method to construct artificial co-transporters, using a porous organic framework membrane which has a relatively disordered stacking structure and rich quaternary ammonium groups paired with counter-ions. This imparts the membrane with extremely narrow pores (∼0.3 nm) and almost no surface charge, enabling size-based high alkaline ion selectivity against other cations, high Cl- selectivity against other anions, but almost no alkaline ion/Cl- selectivity. Such synchronized sieving property allows us to enhance the extraction of high-value cations (Li+) by simply feeding excessive low-value anions (Cl-). As a demonstration, we realized high-flux (0.44 mol m-2 h-1) and highly selective (selectivity: 185) Li+/Mg2+ separation by reversing the current industrial brine-based lithium extraction process, i.e., sieving Li+ before removing NaCl.

Biomimetic ion channels with subnanometer sizes for ion sieving: a mini-review

The remarkable ion selectivity of biological systems has inspired the development of artificial ion channels with Ångström-scale precision, expanding their potential applications in ion separation, energy conversion, and water purification. This mini-review systematically examines fundamental ion-sieving mechanisms operating at the subnanoscale, highlighting advanced fabrication strategies involving synthetic ion channels on lipid bilayers and solid-state ion channels. We further explore membrane material innovations spanning zero-dimensional nanopores to three-dimensional crystalline frameworks, emphasizing structure-function relationships in channel design. The discussion concludes with critical perspectives on scalability challenges and future research directions, outlining pathways toward next-generation sustainable ion sieving technologies.

High-Efficiency Ion Transport in Ultrathin 3D Covalent Organic Framework Nanofluidics

High-efficiency ion transport is essential for both biological and nonbiological processes, including the regulation of cell homeostasis, energy conversion, and mass transfer in chemical industry. Nanofluidic channels are considered ideal platforms for delicate control of ion transport in their unique nanoconfinement, yet currently reported 1D and 2D nanofluidics are subjected to elevated transport resistance due to discontinuous and random channels. Here, we engineer ultrathin, 3D covalent organic framework (3D-COF) nanofluidics featuring continuously interpenetrated pathways and well-ordered pore arrangements, demonstrating superior ion conductance. The energy barrier for ion transport across 3D-COF nanofluidics is exceptionally low, suggesting ultrafast and low-resistance ion movements. Theoretical calculations indicate that 3D-COF nanofluidics facilitate group adsorption to anions, leading to high energy barriers for anion mobility, thus enhancing ion selectivity and high-throughput cation transport. In osmotic energy applications, 3D-COF nanofluidics achieve a power density of 217.7 W m-2 with artificial seawater and river water, potentially scalable to 1238.2 W m-2 under a 500-fold salinity gradient. The proposed 3D-COF nanofluidics offer new avenues for desalination and ion/molecular separation.

Regulation of Ion Binding Sites in Covalent Organic Framework Membranes for Enhanced Selectivity under High Ionic Competition

The strategic spatial positioning of ion affinity sites within biological ion channels and their cooperative binding with the targeted ions are pivotal for enhancing ion recognition and ensuring exceptional selectivity in high ionic competition scenarios. However, the application of these principles to artificial ion channels remains largely unexplored. Herein, we present a series of covalent organic framework (COF) membranes, engineered with oxygen functional groups aligned along the rims of oriented COF pore channels of varying sizes to achieve a precise spatial arrangement of ion affinity sites. A notable COF membrane, featuring subnanometer pores decorated alternately with carbonyl and amide groups, demonstrated outstanding selectivity, achieving a Li/Mg selectivity ratio of 513 under equal mole and electrodialysis conditions. Impressively, as the Mg/Li ratio in the source solution increased to 16.6, the selectivity ratio rose to 833, significantly exceeding the reductions typically seen in conventional selective electrodialysis and nanofiltration methods. Both simulation and experimental analyses indicate that this exceptional selectivity stems from the cooperative binding between the oxygen functional groups and Li+ ions within the confined nanochannels, facilitating the preferential transport of Li+ ions. These findings provide a promising approach for designing selective ion extraction systems that function effectively in highly competitive environments.

Emerging Liquid-Based Memristive Devices for Neuromorphic Computation

To mimic the neural functions of the human brain, developing hardware with natural similarities to the human nervous system is crucial for realizing neuromorphic computing architectures. Owing to their capability to emulate artificial neurons and synapses, memristors are widely regarded as a leading candidate for achieving neuromorphic computing. However, most current memristor devices are solid-state. In contrast, biological nervous systems operate within an aqueous environment, and the human brain accomplishes intelligent behaviors such as information generation, transmission, and memory by regulating ion transport in neuronal cells. To achieve computing systems that are more analogous to biological systems and more energy-efficient, memristor devices based on liquid environments are developed. In contrast to traditional solid-state memristors, liquid-based memristors possess advantages such as anti-interference, low energy consumption, and low heat generation. Simultaneously, they demonstrate excellent biocompatibility, rendering them an ideal option for the next generation of artificial intelligence systems. Numerous experimental demonstrations of liquid-based memristors are reported, showcasing their unique memristive properties and novel neuromorphic functionalities. This review focuses on the recent developments in liquid-based memristors, discussing their operating mechanisms, structures, and functional characteristics. Additionally, the potential applications and development directions of liquid-based memristors in neuromorphic computing systems are proposed.

The Cation-π Interaction in Chemistry and Biology

The cation-π interaction is an important noncovalent binding force that impacts all areas of chemistry and biology. Extensive computational and gas phase experimental studies have established the potential strength and the essential nature of the interaction. Previous reviews have emphasized studies of model systems and a variety of biological examples. This work includes discussion of those areas but emphasizes other areas that are perhaps less well appreciated. These include the novel cation-π binding ability of alkali metals in water; the application of the cation-π interaction to organic synthesis and chemical biology; cooperative behaviors of multiple cation-π interactions, including adhesive proteins from mussels and similar organisms and the formation and modulation of biomolecular condensates (phase separation); and cation-π interactions involved in recognizing DNA/RNA.

Engineering of Covalent Organic Framework Nanosheet Membranes for Fast and Efficient Ion Sieving: Charge-Induced Cation Confined Transport

Artificial membranes with ion-selective nanochannels for high-efficiency mono/divalent ion separation are of great significance in water desalination and lithium-ion extraction, but they remain a great challenge due to the slight physicochemical property differences of various ions. Here, the successful synthesis of two-dimensional TpEBr-based covalent organic framework (COF) nanosheets, and the stacking of them as consecutive membranes for efficient mono/divalent ion separation is reported. The obtained COF nanosheet membranes with intrinsic one-dimensional pores and abundant cationic sites display high permeation rates for monovalent cations (K+, Na+, Li+) of ≈0.1-0.3 mol m-2 h-1, while the value of divalent cations (Ca2+, Mg2+) is two orders of magnitude lower, resulting in an ultrahigh mono/divalent cation separation selectivity up to 130.4, superior to the state-of-the-art ion sieving membranes. Molecular dynamics simulations further confirm that electrostatic interaction controls the confined transport of cations through the cationic COF nanopores, where multivalent cations face i) strong electrostatic repulsion and ii) steric transport hindrance since the large hydrated divalent cations are retarded due to a layer of strongly adsorbed chloride ions at the pore wall, while smaller monovalent cations can swiftly permeate through the nanopores.

Histamine-modulated wettability switching in G-protein-coupled receptor inspired nanochannel for potential drug screening and biosensing

Histamine receptor, one typical G-protein-coupled receptor (GPCR), can be activated by histamine and form the most important drug targets involved in allergy and reflux diseases. Here, we report an artificial model to mimic the wettability-induced activation of natural GPCRs via histamine-modulated enhancement of wettability in a bionic nanochannel. The artificial receptor is constructed by introducing key recognition factors in nature, L-lysine modified fluorescein isothiocyanate (L-lysine-FITC), into a conical nanochannel. The conductance of the L-lysine-FITC-modified nanochannel increases with the histamine-induced wettability enhancement due to the various interactions between histamine and L-lysine-FITC molecules including hydrogen bonding and π-π interactions, as well as the proton transfer reaction. This study represents a crucial step towards the design of artificial GPCRs with wettability-induced activation and provides an opportunity to construct artificial models of GPCRs in a non-lipid environment. The developed artificial receptor has great potential application in medicinal chemistry, biosensors, and healthcare systems.

Accelerating Ion Desolvation via Bioinspired Ion Channel Design in Nonconcentrated Aqueous Electrolytes

In aqueous-based electrochemical energy storage devices, uncontrolled hydrolysis of water at the electrochemical interfaces limits the application of such aqueous batteries or supercapacitors in business. The "water-in-salt" design is a valid strategy to broaden the electrochemical stability window in aqueous electrolytes, but drawbacks such as high manufacturing cost, high electrolyte viscosity, etc., also hinder its development. Here, inspired by biological ion channels in cell membranes, we propose an effective approach to engineer the electrode surface, inducing the desolvation of hydrated ions at the electrochemical interface and inhibiting water decomposition in nonconcentrated electrolytes. The biological engineering strategy enables the induction of controlled desolvation and accelerates the transportation of hydrated ions, e.g., potassium. The subnanometer design (0.8 nm) forces the hydrated potassium ions to shed their solvation shell with a hydration number of only 0.3, while the electrostatic interactions between the pore groups and the potassium ions facilitate their transport. The Zn||Zn cells demonstrate a stable cycling lifespan of over 1000 h at 1 mA cm-2/10 mAh cm-2. This work sheds new light on regulating the electrochemical interfaces in low-concentration aqueous electrolytes for designing aqueous-based energy storage devices.

Modulation of Ion Transport in Nanopores Using Polyethylene Glycol

Ion transport in nanopores is crucial for various biological and technological processes, exhibiting unique behaviors compared to bulk solutions. In this study, we systematically explore how polyethylene glycol (PEG) modulates ion transport within a conical nanopore. Our experiments reveal that introducing PEG into the ionic solution induces a reversal in ion current rectification (ICR). We further investigate the impact of PEG concentration, molecular weight, nanopore size, and cation type on ion transport. Additionally, we assess three different configurations of PEG introduction, identifying diffusive flow driven by an asymmetric cation distribution within the nanopore as a dominant transport mechanism. Our results confirm that the interactions between PEG and cations significantly affect ion transport properties. These findings advance our understanding of macromolecular crowding effects on ion transport and suggest potential applications in iontronic devices and biomolecule sensing.

Comediation of voltage gating and ion charge in MXene membrane for controllable and selective monovalent cation separation

Artificial ion channels with controllable mono/monovalent cation separation fulfill important roles in biomedicine, ion separation, and energy conversion. However, it remains a daunting challenge to develop an artificial ion channel similar to biological ion channels due to ion-ion competitive transport and lack of ion-gating ability of channels. Here, we report a conductive MXene membrane with polydopamine-confined angstrom-scale channels and propose a voltage gating and ion charge comediation strategy to concurrently achieve gated and selective mono/monovalent cation separation. The membrane shows a highly switchable "on-off" ratio of ∼9.9 for K+ transport and an excellent K+/Li+ selectivity of 40.9, outperforming the ion selectivity of reported membranes with electrical gating (typically 1.5 to 6). Theoretical simulations reveal that the introduced high-charge cations such as Mg2+ enable the preferential distribution of target K+ over competing Li+ at the channel entrance, and the surface potential reduces the ionic transport energy barrier for allowing K+ to pass quickly through the channel.

Constructing Flexible Crystalline Porous Organic Salts via a Zwitterionic Strategy

The unique ionic channels and highly polar pore structures have distinguished crystalline porous organic salts (CPOSs) from conventional porous frameworks in the past decade. Up to now, CPOSs were all constructed by a monoionic strategy, in which two types of building units individually bearing anionic or cationic groups were introduced, thus increasing complexity in the synthesis of CPOSs. In this study, by utilizing stereoisomeric compounds of TPE-NS-Z or TPE-NS-E bearing both anionic and cationic groups as a single building unit, the zwitterionic strategy was proven feasible in constructing CPOSs. Benefiting from the single building unit, the zwitterionic strategy simplified the preparation process and reduced the difficulty in studying the aggregation behavior of building units into CPOSs. And also, this novel strategy enabled precise control of the finally obtained CPOSs through fine-tuning of the initial building units. Surprisingly, the special parallel/vertical alternated stacking mode and unique ionic interaction networks in the crystal structure provided the flexible pore characteristic of CPOS-E, which further guaranteed the multitime controllable release of highly polar chemicals in different solvents.

Covalent organic framework membranes with vertically aligned nanorods for efficient separation of rare metal ions

Covalent organic frameworks (COFs) have emerged as promising platforms for membrane separations, while remaining challenging for separating ions in a fast and selective way. Here, we propose a concept of COF membranes with vertically aligned nanorods for efficient separation of rare metal ions. A quaternary ammonium-functionalized monomer is rationally designed to synthesize COF layers on porous substrates via interfacial synthesis. The COF layers possess an asymmetric structure, in which the upper part displays vertically aligned nanorods, while the lower part exhibits an ultrathin dense layer. The vertically aligned nanorods enlarge contact areas to harvest water and monovalent ions, and the ultrathin dense layer enables both high permeability and selectivity. The resulting membranes exhibit exceptional separation performances, for instance, a Cs+ permeation rate of 0.33 mol m-2 h-1, close to the value in porous substrates, and selectivities with Cs+/La3+ up to 75.9 and 69.8 in single and binary systems, highlighting the great potentials in the separation of rare metal ions.

Effectively Sieving Alkali Metal Ions Using Functionalized Graphene Oxide Membranes by Exploiting Water-Repellent Interactions

Sieving membranes capable of discerning different alkali metal ions are important for many technologies, such as energy, environment, and life science. Recently, two-dimensional (2D) materials have been extensively explored for the creation of sieving membranes with angstrom-scale channels. However, because of the same charge and similar hydrated sizes, mostly laminated membranes typically show low selectivity (<10). Herein, we report a facile and scalable method for functionalizing graphene oxide (GO) laminates by dually grafting cations and water-repellent dimethylsiloxane (DMDMS) molecules to achieve high selectivities of ∼50 and ∼20 toward the transport of Cs+/Li+ and K+/Li+ ion pairs, surpassing many of the state-of-the-art laminated membranes. The enhanced selectivity for alkali metal ions can be credited to a dual impact: (i) strong hydrophobic interactions between the incident cations' hydration shells and the water-repellent DMDMS; (ii) the efficient screening of electrostatic interactions that hamper selectivity.

A Bioinspired Membrane with Ultrahigh Li+/Na+ and Li+/K+ Separations Enables Direct Lithium Extraction from Brine

Membranes with precise Li+/Na+ and Li+/K+ separations are imperative for lithium extraction from brine to address the lithium supply shortage. However, achieving this goal remains a daunting challenge due to the similar valence, chemical properties, and subtle atomic-scale distinctions among these monovalent cations. Herein, inspired by the strict size-sieving effect of biological ion channels, a membrane is presented based on nonporous crystalline materials featuring structurally rigid, dimensionally confined, and long-range ordered ion channels that exclusively permeate naked Li+ but block Na+ and K+. This naked-Li+-sieving behavior not only enables unprecedented Li+/Na+ and Li+/K+ selectivities up to 2707.4 and 5109.8, respectively, even surpassing the state-of-the-art membranes by at least two orders of magnitude, but also demonstrates impressive Li+/Mg2+ and Li+/Ca2+ separation capabilities. Moreover, this bioinspired membrane has to be utilized for creating a one-step lithium extraction strategy from natural brines rich in Na+, K+, and Mg2+ without utilizing chemicals or creating solid waste, and it simultaneously produces hydrogen. This research has proposed a new type of ion-sieving membrane and also provides an envisioning of the design paradigm and development of advanced membranes, ion separation, and lithium extraction.

Using Nanoscale Passports To Understand and Unlock Ion Channels as Gatekeepers of the Cell

Natural ion channels are proteins embedded in the cell membrane that control many aspects of cell and human physiology by acting as gatekeepers, regulating the flow of ions in and out of cells. Advances in nanotechnology have influenced the methods for studying ion channels in vitro, as well as ways to unlock the delivery of therapeutics by modulating them in vivo. This review provides an overview of nanotechnology-enabled approaches for ion channel research with a focus on the synthesis and applications of synthetic ion channels. Further, the uses of nanotechnology for therapeutic applications are critically analyzed. Finally, we provide an outlook on the opportunities and challenges at the intersection of nanotechnology and ion channels. This work highlights the key role of nanoscale interactions in the operation and modulation of ion channels, which may prompt insights into nanotechnology-enabled mechanisms to study and exploit these systems in the near future.

A physical derivation of high-flux ion transport in biological channel via quantum ion coherence

Biological ion channels usually conduct the high-flux transport of 107 ~ 108 ions·s-1; however, the underlying mechanism is still lacking. Here, by applying the KcsA potassium channel as a typical example, and performing multitimescale molecular dynamics simulations, we demonstrate that there is coherence of the K+ ions confined in biological channels, which determines transport. The coherent oscillation state of confined K+ ions with a nanosecond-level lifetime in the channel dominates each transport event, serving as the physical basis for the high flux of ~108 ions∙s-1. The coherent transfer of confined K+ ions only takes several picoseconds and has no perturbation effect on the ion coherence, acting as the directional key of transport. Such ion coherence is allowed by quantum mechanics. An increase in the coherence can significantly enhance the ion conductance. These findings provide a potential explanation from the perspective of coherence for the high-flux ion transport with ultralow energy consumption of biological channels.

Zn-ion ultrafluidity via bioinspired ion channel for ultralong lifespan Zn-ion battery

Rechargeable aqueous Zn-ion batteries have been deemed a promising energy storage device. However, the dendrite growth and side reactions have hindered their practical application. Herein, inspired by the ultrafluidic and K+ ion-sieving flux through enzyme-gated potassium channels (KcsA) in biological plasma membranes, a metal-organic-framework (MOF-5) grafted with -ClO4 groups (MOF-ClO4) as functional enzymes is fabricated to mimic the ultrafluidic lipid-bilayer structure for gating Zn2+ 'on' and anions 'off' states. The MOF-ClO4 achieved perfect Zn2+/SO4 2- selectivity (∼10), enhanced Zn2+ transfer number ([Formula: see text]) and the ultrafluidic Zn2+ flux (1.9 × 10-3 vs. 1.67 mmol m-2 s-1 for KcsA). The symmetric cells based on MOF-ClO4 achieve a lifespan of over 5400 h at 10 mA cm-2/20 mAh cm-2. Specifically, the performance of the PMCl-Zn//V2O5 pouch cell keeps 81% capacity after 2000 cycles at 1 A g-1. The regulated ion transport, by learning from a biological plasma membrane, opens a new avenue towards ultralong lifespan aqueous batteries.

High-efficiency dysprosium-ion extraction enabled by a biomimetic nanofluidic channel

Biological ion channels exhibit high selectivity and permeability of ions because of their asymmetrical pore structures and surface chemistries. Here, we demonstrate a biomimetic nanofluidic channel (BNC) with an asymmetrical structure and glycyl-L-proline (GLP) -functionalization for ultrafast, selective, and unidirectional Dy3+ extraction over other lanthanide (Ln3+) ions with very similar electronic configurations. The selective extraction mainly depends on the amplified chemical affinity differences between the Ln3+ ions and GLPs in nanoconfinement. In particular, the conductivities of Ln3+ ions across the BNC even reach up to two orders of magnitude higher than in a bulk solution, and a high Dy3+/Nd3+ selectivity of approximately 60 could be achieved. The designed BNC can effectively extract Dy3+ ions with ultralow concentrations and thereby purify Nd3+ ions to an ultimate content of 99.8 wt.%, which contribute to the recycling of rare earth resources and environmental protection. Theoretical simulations reveal that the BNC preferentially binds to Dy3+ ion due to its highest affinity among Ln3+ ions in nanoconfinement, which attributes to the coupling of ion radius and coordination matching. These findings suggest that BNC-based ion selectivity system provides alternative routes to achieving highly efficient lanthanide separation.

Stimuli-Responsive Ion Transport Regulation in Nanochannels by Adhesion-Induced Functionalization of Macroscopic Outer Surface

Responsive regulation of ion transport through nanochannels is crucial in the design of smart nanofluidic devices for sequencing, sensing, and water-energy nexus. Functionalization of the inner wall of the nanochannel enhances interaction with ions and fluid but restricts versatile chemical approaches and accurate characterizations of fluidic interfaces. Herein, we reveal a responsive regulating mechanism of ion transport through nanochannels by polydopamine (PDA)-induced functionalization on the macroscopic outer surface of nanochannels. Responsive molecules were codeposited with PDA on the outer surface of nanochannels and formed a valve of nanometer thickness to manually manipulate ion transport by changing its gap spacing, surface charge, and wettability under external stimulus. The response ratio can be up to 100-fold by maximizing the proportion of responsive molecules on the outer surface. Laminating the codepositions of different responsive molecules with PDA on the channel's outer surface produces multiple responses. A nearly universal adhesion of PDA with responsive molecules on the open outer surface induces nanochannels responsive to different external stimuli with variable response ratios and arbitrary combinations. The results challenge the primary role of functionalization on the nanoconfined interface of nanofluidics and open opportunities for developing new-style nanofluidic devices through the functionalization of macroscopic interface.

Electric Eel Biomimetics for Energy Storage and Conversion

The electric eel is known as the most powerful creature to generate electricity with a discharge voltage up to 860 V and peak current up to 1 A. These surprising properties are the results of billions of years of evolution on the electrical biological structure and bulk, and now have triggered great research interest in electric eel biomimetics for designing innovated configurations and components of energy storage and conversion devices. In this review, first, the bioelectrical behavior of electric eels is surveyed, followed by the physiological structure to reveal the discharge characteristics and principles of electric organs and electrocytes. Additionally, underlying electrochemical mechanisms and models for calculating the potential and current of electrocytes are presented. Central to this review is the recent progress of electric-eel-inspired innovations and applications for energy storage and conversion, particularly including novel power sources, triboelectric nanogenerators, and nanochannel ion-selective membranes for salinity gradient energy harvesting. Finally, insights on the challenges at the moment and the perspectives on the future research prospects are critically compiled. It is suggested that energy-related electric eel biomimetics will greatly boost the development of next-generation high performance, green, and functional electronics.

Toward Selective Transport of Monovalent Metal Ions with High Permeability Based on Crown Ether-Encapsulated Metal-Organic Framework Sub-Nanochannels

Achieving selective transport of monovalent metal ions with high precision and permeability analogues to biological protein ion channels has long been explored for fundamental research and various applications, such as ion sieving, mineral extraction, and energy harvesting and conversion. However, it still remains a significant challenge to construct artificial nanofluidic devices to realize the trade-off effects between selective ion transportation and high ion permeability. In this work, we report a bioinspired functional micropipet with in situ growth of crown ether-encapsulated metal-organic frameworks (MOFs) inside the tip and realize selective transport of monovalent metal ions. The functional ion-selective micropipet with sub-nanochannels was constructed by the interfacial growth method with the formation of composite MOFs consisting of ZIF-8 and 15-crown-5. The resulting micropipet device exhibited obvious monovalent ion selectivity and high flux of Li+ due to the synergistic effects of size sieving in subnanoconfined space and specific coordination of 15-crown-5 toward Na+. The selectivity of Li+/Na+, Li+/K+, Li+/Ca2+, and Li+/Mg2+ with 15-crown-5@ZIF-8-functionalized micropipet reached 3.9, 5.2, 105.8, and 122.4, respectively, which had an obvious enhancement compared to that with ZIF-8. Notably, the ion flux of Li+ can reach up to 93.8 ± 3.6 mol h-1·m-2 that is much higher than previously reported values. Furthermore, the functional micropipet with 15-crown-5@ZIF-8 sub-nanochannels exhibited stable Li+ selectivity under various conditions, such as different ion concentrations, pH values, and mixed ion solutions. This work not only provides new opportunities for the development of MOF-based nanofluidic devices for selective ion transport but also facilitates the promising practical applications in lithium extraction from salt-like brines, sewage treatment, and other related aspects.

PNA-Functionalized, Silica Nanowires-Filled Glass Microtube for Ultrasensitive and Label-Free Detection of miRNA-21

MicroRNAs (miRNAs) are endogenous and noncoding single-stranded RNA molecules with a length of approximately 18-25 nucleotides, which play an undeniable role in early cancer screening. Therefore, it is very important to develop an ultrasensitive and highly specific method for detecting miRNAs. Here, we present a bottom-up assembly approach for modifying glass microtubes with silica nanowires (SiNWs) and develop a label-free sensing platform for miRNA-21 detection. The three-dimensional (3D) networks formed by SiNWs make them abundant and highly accessible sites for binding with peptide nucleic acid (PNA). As a receptor, PNA has no phosphate groups and exhibits an overall electrically neutral state, resulting in a relatively small repulsion between PNA and RNA, which can improve the hybridization efficiency. The SiNWs-filled glass microtube (SiNWs@GMT) sensor enables ultrasensitive, label-free detection of miRNA-21 with a detection limit as low as 1 aM at a detection range of 1 aM-100 nM. Noteworthy, the sensor can still detect miRNA-21 in the range of 102-108 fM in complex solutions containing 1000-fold homologous interference of miRNAs. The high anti-interference performance of the sensor enables it to specifically recognize target miRNA-21 in the presence of other miRNAs and distinguish 1-, 3-mismatch nucleotide sequences. Significantly, the sensor platform is able to detect miRNA-21 in the lysate of breast cancer cell lines (e.g., MCF-7 cells and MDA-MB-231 cells), indicating that it has good potential in the screening of early breast cancers.

Electrochemical coupling in subnanometer pores/channels for rechargeable batteries

Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions.

Bio-Inspired Subnanofluidics: Advanced Fabrication and Functionalization

Biological ion channels can realize high-speed and high-selective ion transport through the protein filter with the sub-1-nanometer channel. Inspired by biological ion channels, various kinds of artificial subnanopores, subnanochannels, and subnanoslits with improved ion selectivity and permeability are recently developed for efficient separation, energy conversion, and biosensing. This review article discusses the advanced fabrication and functionalization methods for constructing subnanofluidic pores, channels, tubes, and slits, which have shown great potential for various applications. Novel fabrication methods for producing subnanofluidics, including top-down techniques such as electron beam etching, ion irradiation, and electrochemical etching, as well as bottom-up approaches starting from advanced microporous frameworks, microporous polymers, lipid bilayer embedded subnanochannels, and stacked 2D materials are well summarized. Meanwhile, the functionalization methods of subnanochannels are discussed based on the introduction of functional groups, which are classified into direct synthesis, covalent bond modifications, and functional molecule fillings. These methods have enabled the construction of subnanochannels with precise control of structure, size, and functionality. The current progress, challenges, and future directions in the field of subnanofluidic are also discussed.

Charge-Assisted Ionic Hydrogen-Bonded Organic Frameworks: Designable and Stabilized Multifunctional Materials

Hydrogen-bonded organic frameworks (HOFs) are a class of crystalline framework materials assembled by hydrogen bonds. HOFs have the advantages of high crystallinity, mild reaction conditions, good solution processability, and reproducibility. Coupled with the reversibility and flexibility of hydrogen bonds, HOFs can be assembled into a wide diversity of crystalline structures. Since the bonding energy of hydrogen bonds is lower than that of ligand and covalent bonds, the framework of HOFs is prone to collapse after desolventisation and the stability is not high, which limits the development and application of HOFs. In recent years, numerous stable and functional HOFs have been developed by π-π stacking, highly interpenetrated networks, charge-assisted, ligand-bond-assisted, molecular weaving, and covalent cross-linking. Charge-assisted ionic HOFs introduce electrostatic attraction into HOFs to improve stability while enriching structural diversity and functionality. In this paper, we review the development, the principles of rational design and assembly of charge-assisted ionic HOFs, and introduces the different building block construction modes of charge-assisted ionic HOFs. Highlight the applications of charge-assisted ionic HOFs in gas adsorption and separation, proton conduction, biological applications, etc., and prospects for the diverse design of charge-assisted ionic HOFs structures and multifunctional applications.

Regulating ion affinity and dehydration of metal-organic framework sub-nanochannels for high-precision ion separation

Membrane consisting of ordered sub-nanochannels has been pursued in ion separation technology to achieve applications including desalination, environment management, and energy conversion. However, high-precision ion separation has not yet been achieved owing to the lack of deep understanding of ion transport mechanism in confined environments. Biological ion channels can conduct ions with ultrahigh permeability and selectivity, which is inseparable from the important role of channel size and "ion-channel" interaction. Here, inspired by the biological systems, we report the high-precision separation of monovalent and divalent cations in functionalized metal-organic framework (MOF) membranes (UiO-66-(X)2, X = NH2, SH, OH and OCH3). We find that the functional group (X) and size of the MOF sub-nanochannel synergistically regulate the ion binding affinity and dehydration process, which is the key in enlarging the transport activation energy difference between target and interference ions to improve the separation performance. The K+/Mg2+ selectivity of the UiO-66-(OCH3)2 membrane reaches as high as 1567.8. This work provides a gateway to the understanding of ion transport mechanism and development of high-precision ion separation membranes.

Archaea-Inspired Switchable Nanochannels for On-Demand Lithium Detection by pH Activation

With the rapid development of the lithium ion battery industry, emerging lithium (Li) enrichment in nature has attracted ever-growing attention due to the biotoxicity of high Li levels. To date, fast lithium ion (Li+) detection remains urgent but is limited by the selectivity, sensitivity, and stability of conventional technologies based on passive response processes. In nature, archaeal plasma membrane ion exchangers (NCLX_Mj) exhibit Li+-gated multi/monovalent ion transport behavior, activated by different stimuli. Inspired by NCLX_Mj, we design a pH-controlled biomimetic Li+-responsive solid-state nanochannel system for on-demand Li+ detection using 2-(2-hydroxyphenyl)benzoxazole (HPBO) units as Li+ recognition groups. Pristine HPBO is not reactive to Li+, whereas negatively charged HPBO enables specific Li+ coordination under alkaline conditions to decrease the ion exchange capacity of nanochannels. On-demand Li+ detection is achieved by monitoring the decline in currents, thereby ensuring precise and stable Li+ recognition (>0.1 mM) in the toxic range of Li+ concentration (>1.5 mM) for human beings. This work provides a new approach to constructing Li+ detection nanodevices and has potential for applications of Li-related industries and medical services.

Enhancing ion selectivity by tuning solvation abilities of covalent-organic-framework membranes

Understanding the molecular-level mechanisms involved in transmembrane ion selectivity is essential for optimizing membrane separation performance. In this study, we reveal our observations regarding the transmembrane behavior of Li+ and Mg2+ ions as a response to the changing pore solvation abilities of the covalent-organic-framework (COF) membranes. These abilities were manipulated by adjusting the lengths of the oligoether segments attached to the pore channels. Through comparative experiments, we were able to unravel the relationships between pore solvation ability and various ion transport properties, such as partitioning, conduction, and selectivity. We also emphasize the significance of the competition between Li+ and Mg2+ with the solvating segments in modulating selectivity. We found that increasing the length of the oligoether chain facilitated ion transport; however, it was the COF membrane with oligoether chains containing two ethylene oxide units that exhibited the most pronounced discrepancy in transmembrane energy barrier between Li+ and Mg2+, resulting in the highest separation factor among all the evaluated membranes. Remarkably, under electro-driven binary-salt conditions, this specific COF membrane achieved an exceptional Li+/Mg2+ selectivity of up to 1352, making it one of the most effective membranes available for Li+/Mg2+ separation. The insights gained from this study significantly contribute to advancing our understanding of selective ion transport within confined nanospaces and provide valuable design principles for developing highly selective COF membranes.

Single Idiosyncratic Ionic Generator Working in Iso-Osmotic Solutions Via Ligand Confined Assembled in Gaps Between Nanosheets

Numerous reported bioinspired osmotic energy conversion systems employing cation-/anion-selective membranes and solutions with different salinity are actually far from the biological counterpart. The iso-osmotic power generator with the specific ionic permselective channels (e.g., K+ or Na+ channels) which just allow specific ions to get across and iso-osmotic solutions still remain challenges. Inspired by nature, we report a bioinspired K+ -channel by employing a K+ selective ligand, 1,1,1-tris{[(2'-benzylaminoformyl)phenoxy]methyl}ethane (BMP) and graphene oxide membrane. Specifically, the K+ and Na+ selectivity of the prepared system could reach up to ≈17.8, and the molecular dynamics simulation revealed that the excellent permselectivity of K+ mainly stemmed from the formed suitable channel size. Thus, we assembled the K+ -selective iso-osmotic power generator (KSIPG) with the power density up to ≈15.1 mW/m2 between equal concentration solutions, which is higher than traditional charge-selective osmotic power generator (CSOPG). The proposed strategy has well shown the realizable approach to construct single-ion selective channels-based highly efficient iso-osmotic energy conversion systems and would surely inspire new applications in other fields, including self-powered systems and medical materials, etc.

Highly Selective Lithium Transport through Crown Ether Pillared Angstrom Channels

Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom-sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li+ selectivity. The pillared channels and crown ether have an angstrom-scale size. The crown ether specifically allows the low-barrier transport of Li+ . The channels attract and enrich Li+ ions by up to orders of magnitude. As a result, our material sieves Li+ out of various common ions such as Na+ , K+ , Ca2+ , Mg2+ and Al3+ . Moreover, by spontaneously enriching Li+ ions, it realizes an effective Li+ /Na+ selectivity of 1422 in artificial seawater where the Li+ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.

Crystalline porous organic salts

Crystalline porous organic salts (CPOSs), formed by the self-assembly of organic acids and organic bases through ionic bonding, possess definite structures and permanent porosity and have rapidly emerged as an important class of porous organic materials in recent years. By rationally designing and controlling tectons, acidity/basicity (pKa), and topology, stable CPOSs with permanent porosity can be efficiently constructed. The characteristics of ionic bonds, charge-separated highly polar nano-confined channels, and permanent porosity endow CPOSs with unique physicochemical properties, offering extensive research opportunities for exploring their functionalities and application scenarios. In this review, we systematically summarize the latest progress in CPOS research, describe the synthetic strategies for synthesizing CPOSs, delineate their structural characteristics, and highlight the differences between CPOSs and hydrogen-bonded organic frameworks (HOFs). Furthermore, we provide an overview of the potential applications of CPOSs in areas such as negative linear compression (NLC), proton conduction, rapid transport of CO2, selective and rapid transport of K+ ions, atmospheric water harvesting (AWH), gas sorption, molecular rotors, fluorescence modulation, room-temperature phosphorescence (RTP) and catalysis. Finally, the challenges and future perspectives of CPOSs are presented.

Covalently Functionalized Nanopores for Highly Selective Separation of Monovalent Ions

Biological ion channels possess prominent ion transport performances attributed to their critical chemical groups across the continuous nanoscale filters. However, it is still a challenge to imitate these sophisticated performances in artificial nanoscale systems. Herein, this work develops the strategy to fabricate functionalized graphene nanopores in pioneer based on the synergistic regulation of the pore size and chemical properties of atomically thin confined structure through decoupling etching combined with in situ covalent modification. The modified graphene nanopores possess asymmetric ion transport behaviors and efficient monovalent metal ions sieving (K+ /Li+ selectivity ≈48.6). Meanwhile, it also allows preferential transport for cations, the resulting membranes exhibit a K+ /Cl- selectivity of 76 and a H+ /Cl- selectivity of 59.3. The synergistic effects of steric hindrance and electrostatic interactions imposing a higher energy barrier for Cl- or Li+ across nanopores lead to ultra-selective H+ or K+ transport. Further, the functionalized graphene nanopores generate a power density of 25.3 W m-2 and a conversion efficiency of 33.9%, showing potential application prospects in energy conversion. The theoretical studies quantitatively match well with the experimental results. The feasible preparation of functionalized graphene nanopores paves the way toward direct investigation on ion transport mechanism and advanced design in devices.

Ultralow Energy Consumption Angstrom-Fluidic Memristor

The emergence of nanofluidic memristors has made a giant leap to mimic the neuromorphic functions of biological neurons. Here, we report neuromorphic signaling using Angstrom-scale funnel-shaped channels with poly-l-lysine (PLL) assembled at nano-openings. We found frequency-dependent current-voltage characteristics under sweeping voltage, which represents a diode in low frequencies, but it showed pinched current hysteresis as frequency increases. The current hysteresis is strongly dependent on pH values but weakly dependent on salt concentration. We attributed the current hysteresis to the entropy barrier of PLL molecules entering and exiting the Angstrom channels, resulting in reversible voltage-gated open-close state transitions. We successfully emulated the synaptic adaptation of Hebbian learning using voltage spikes and obtained a minimum energy consumption of 2-23 fJ in each spike per channel. Our findings pave a new way to mimic neuronal functions by Angstrom channels in low energy consumption.

Designing artificial ion channels with strict K+/Na+ selectivity toward next-generation electric-eel-mimetic ionic power generation

A biological potassium channel is >1000 times more permeable to K+ than to Na+ and exhibits a giant permeation rate of ∼108 ions/s. It is a great challenge to construct artificial potassium channels with such high selectivity and ion conduction rate. Herein, we unveil a long-overlooked structural feature that underpins the ultra-high K+/Na+ selectivity. By carrying out massive molecular dynamics simulation for ion transport through carbonyl-oxygen-modified bi-layer graphene nanopores, we find that the twisted carbonyl rings enable strict potassium selectivity with a dynamic K+/Na+ selectivity ratio of 1295 and a K+ conduction rate of 3.5 × 107 ions/s, approaching those of the biological counterparts. Intriguingly, atomic trajectories of K+ permeation events suggest a dual-ion transport mode, i.e. two like-charged potassium ions are successively captured by the nanopores in the graphene bi-layer and are interconnected by sharing one or two interlayer water molecules. The dual-ion behavior allows rapid release of the exiting potassium ion via a soft knock-on mechanism, which has previously been found only in biological ion channels. As a proof-of-concept utilization of this discovery, we propose a novel way for ionic power generation by mixing KCl and NaCl solutions through the bi-layer graphene nanopores, termed potassium-permselectivity enabled osmotic power generation (PoPee-OPG). Theoretically, the biomimetic device achieves a very high power density of >1000 W/m2 with graphene sheets of <1% porosity. This study provides a blueprint for artificial potassium channels and thus paves the way toward next-generation electric-eel-mimetic ionic power generation.

Molecularly Selective Polymer Interfaces for Electrochemical Separations

The molecular design of polymer interfaces has been key for advancing electrochemical separation processes. Precise control of molecular interactions at electrochemical interfaces has enabled the removal or recovery of charged species with enhanced selectivity, capacity, and stability. In this Perspective, we provide an overview of recent developments in polymer interfaces applied to liquid-phase electrochemical separations, with a focus on their role as electrosorbents as well as membranes in electrodialysis systems. In particular, we delve into both the single-site and macromolecular design of redox polymers and their use in heterogeneous electrochemical separation platforms. We highlight the significance of incorporating both redox-active and non-redox-active moieties to tune binding toward ever more challenging separations, including structurally similar species and even isomers. Furthermore, we discuss recent advances in the development of selective ion-exchange membranes for electrodialysis and the critical need to control the physicochemical properties of the polymer. Finally, we share perspectives on the challenges and opportunities in electrochemical separations, ranging from the need for a comprehensive understanding of binding mechanisms to the continued innovation of electrochemical architectures for polymer electrodes.

Interfacial Self-assembly of Chiral Selenide Nanomembrane for Enantiospecific Recognition

Here, we report the synthesis of chiral selenium nanoparticles (NPs) using cysteine and the interfacial assembly strategy to generate a self-assembled nanomembrane on a large-scale with controllable morphology and handedness. The selenide (Se) NPs exhibited circular dichroism (CD) bands in the ultraviolet and visible region with a maximum intensity of 39.96 mdeg at 388 nm and optical anisotropy factors (g-factors) of up to 0.0013 while a self-assembled monolayer nanomembrane exhibited symmetrical CD approaching 72.8 mdeg at 391 nm and g-factors up to 0.0034. Analysis showed that a photocurrent of 20.97±1.55 nA was generated by the D-nanomembrane when irradiated under light while the L-nanomembrane generated a photocurrent of 20.58±1.36 nA. Owing to the asymmetric intensity of the photocurrent with respect to the handedness of the nanomembrane, an ultrasensitive recognition of enantioselective kynurenine (Kyn) was achieved by the ten-layer (10L) D-nanomembrane exhibiting a photocurrent for L-kynurenine (L-Kyn) that was 8.64-fold lower than that of D-Kyn, with a limit of detection (LOD) of 0.0074 nM for the L-Kyn, which was attributed to stronger affinity between L-Kyn and D-Se NPs. Noticeably, the chiral Se nanomembrane precisely distinguished L-Kyn in serum and cerebrospinal fluid samples from Alzheimer's disease patients and healthy subjects.

Extreme Ion-Transport Inorganic 2D Membranes for Nanofluidic Applications

Inorganic 2D materials offer a new approach to controlling mass diffusion at the nanoscale. Controlling ion transport in nanofluidics is key to energy conversion, energy storage, water purification, and numerous other applications wherein persistent challenges for efficient separation must be addressed. The recent development of 2D membranes in the emerging field of energy harvesting, water desalination, and proton/Li-ion production in the context of green energy and environmental technology is herein discussed. The fundamental mechanisms, 2D membrane fabrication, and challenges toward practical applications are highlighted. Finally, the fundamental issues of thermodynamics and kinetics are outlined along with potential membrane designs that must be resolved to bridge the gap between lab-scale experiments and production levels.

Guanidinium-based covalent organic framework membrane for single-acid recovery

Acids are extensively used in contemporary industries. However, time-consuming and environmentally unfriendly processes hinder single-acid recovery from wastes containing various ionic species. Although membrane technology can overcome these challenges by efficiently extracting analytes of interest, the associated processes typically exhibit inadequate ion-specific selectivity. In this regard, we rationally designed a membrane with uniform angstrom-sized pore channels and built-in charge-assisted hydrogen bond donors that preferentially conducted HCl while exhibiting negligible conductance for other compounds. The selectivity originates from the size-screening ability of angstrom-sized channels between protons and other hydrated cations. The built-in charge-assisted hydrogen bond donor enables the screening of acids by exerting host-guest interactions to varying extents, thus acting as an anion filter. The resulting membrane exhibited exceptional permeation for protons over other cations and for Cl^- over SO₄^2- and H_nPO₄^(3-n)- with selectivities up to 4334 and 183, respectively, demonstrating prospects for HCl extraction from waste streams. These findings will aid in designing advanced multifunctional membranes for sophisticated separation.

Beyond steric selectivity of ions using ångström-scale capillaries

Ion-selective channels play a key role in physiological processes and are used in many technologies. Although biological channels can efficiently separate same-charge ions with similar hydration shells, it remains a challenge to mimic such exquisite selectivity using artificial solid-state channels. Although there are several nanoporous membranes that show high selectivity with respect to certain ions, the underlying mechanisms are based on the hydrated ion size and/or charge. There is a need to rationalize the design of artificial channels to make them capable of selecting between similar-sized same-charge ions, which, in turn, requires an understanding of why and how such selectivity can occur. Here we study ångström-scale artificial channels made by van der Waals assembly, which are comparable in size with typical ions and carry little residual charge on the channel walls. This allows us to exclude the first-order effects of steric- and Coulomb-based exclusion. We show that the studied two-dimensional ångström-scale capillaries can distinguish between same-charge ions with similar hydrated diameters. The selectivity is attributed to different positions occupied by ions within the layered structure of nanoconfined water, which depend on the ion-core size and differ for anions and cations. The revealed mechanism points at the possibilities of ion separation beyond simple steric sieving.

Bioinspired design of Na-ion conduction channels in covalent organic frameworks for quasi-solid-state sodium batteries

Solid polymer electrolytes are considered among the most promising candidates for developing practical solid-state sodium batteries. However, moderate ionic conductivity and narrow electrochemical windows hinder their further application. Herein, inspired by the Na⁺/K⁺ conduction in biological membranes, we report a (-COO^-)-modified covalent organic framework (COF) as a Na-ion quasi-solid-state electrolyte with sub-nanometre-sized Na⁺ transport zones (6.7-11.6 Å) created by adjacent -COO^- groups and COF inwalls. The quasi-solid-state electrolyte enables selective Na⁺ transport along specific areas that are electronegative with sub-nanometre dimensions, resulting in a Na⁺ conductivity of 1.30×10^-4 S cm^-1 and oxidative stability of up to 5.32 V (versus Na⁺/Na) at 25 ± 1 °C. Testing the quasi-solid-state electrolyte in Na||Na₃V₂(PO₄)₃ coin cell configuration demonstrates fast reaction dynamics, low polarization voltages, and a stable cycling performance over 1000 cycles at 60 mA g^-1 and 25 ± 1 °C with a 0.0048% capacity decay per cycle and a final discharge capacity of 83.5 mAh g^-1.

An Air-Rechargeable Zn Battery Enabled by Organic-Inorganic Hybrid Cathode

Self-charging power systems collecting energy harvesting technology and batteries are attracting extensive attention. To solve the disadvantages of the traditional integrated system, such as highly dependent on energy supply and complex structure, an air-rechargeable Zn battery based on MoS2/PANI cathode is reported. Benefited from the excellent conductivity desolvation shield of PANI, the MoS2/PANI cathode exhibits ultra-high capacity (304.98 mAh g-1 in N2 and 351.25 mAh g-1 in air). In particular, this battery has the ability to collect, convert and store energy simultaneously by an air-rechargeable process of the spontaneous redox reaction between the discharged cathode and O2 from air. The air-rechargeable Zn batteries display a high open-circuit voltage (1.15 V), an unforgettable discharge capacity (316.09 mAh g-1 and the air-rechargeable depth is 89.99%) and good air-recharging stability (291.22 mAh g-1 after 50 air recharging/galvanostatic current discharge cycle). Most importantly, both our quasi-solid zinc ion batteries and batteries modules have excellent performance and practicability. This work will provide a promising research direction for the material design and device assembly of the next-generation self-powered system.